The present invention relates a combustion control system which properly controls a fuel injection timing, an ignition timing and an EGR (exhaust gas recirculation) according to a fuel property such as a center number or octane number of fuel using in an internal combustion engine.
Japanese Examined Utility Model Application No. 3-45181 discloses a cetane number sensor for detecting a fuel property of fuel used in an internal combustion engine. By determining a centane number of light oil actually used by means of the cetane number sensor, a proper fuel injection is executed according to the determined fuel property to stably operate the internal combustion engine.
A cetane number determination method employing this cetane number sensor is executed on the assumption that a viscosity and a center number of light oil have a proportional relationship. As a means for measuring a viscosity of light oil, there are provided a pendulum which sinks in light oil of a fuel tank by gravity and a sink time measuring mechanism which measures a sink time of the pendulum affected by viscosity. The viscosity of the light oil is determined from the sink time, and a cetane number of the light oil is determined by correcting the obtained viscosity in temperature.
Japanese Published Patent Application No. 11-107820 discloses a combustion control system of a diesel engine. This combustion control system comprises an in-cylinder pressure sensor for detecting an ignition timing, in order to vary the ignition timing or an EGR ratio when an actual ignition timing deviates from a target ignition timing due to dispersion of a cetane number of fuel in markets and the like. Consequently, this system is arranged such that the fuel property such as a centane number influences a difference between the actual ignition timing and the target ignition timing.